This invention relates to “on-demand” fuel pumps, and more particularly, to such a fuel pump which is capable of delivering fuel at different output pressure levels depending upon engine conditions.
In co-assigned U.S. Pat. No. 5,961,293, there is described an in-tank fuel pump assembly for use with an internal combustion engine. The pump assembly draws low pressure fuel from the fuel tank in which the assembly is installed and delivers fuel at a high pressure to an internal combustion engine. Fuel demand varies depending upon a variety of factors including whether the vehicle is accelerating, decelerating, or traveling at a constant speed, the altitude at which the vehicle is moving, air temperature, and whether the vehicle is traveling on a straight path, ascending or descending, or turning. Modern electronic engine control systems are responsive to inputs from various sensors to control operation of the fuel pump so the pump delivers only the amount of fuel required by the engine at any one time; more or less fuel being supplied as circumstances warrant. This is referred to as “on demand” fuel delivery.
Heretofore, the pressure at which the fuel pump delivered fuel to the engine has been a single pressure level value; e.g. 15 psi, 30 psi, etc. Now, however, it has been found to be desirable to vary both the pressure at which fuel is delivered to the engine, as well as the amount of fuel delivered. Current fuel pump assemblies cannot provide this capability, thereby limiting their performance capabilities and the efficiency of the fuel delivery system of which they are a part. Rather, to achieve a multiple pressure capability, multiple pressure regulators and/or multiple fuel flow regulators are required within the fuel system. These add both cost and complexity to the system.